C++: 'adding references' to namespaces (and class libraries)?

I'm curious about adding references through the "Property Pages" dialog in Visual Studio C++. Specifically adding 'class libraries' and, even more so, 'namespaces'.

In what I'm reading it says that both 'class library's and 'namespaces' can be referenced in this way-- I can see what the reference for 'class libraries' are for (bringing in a dll to be able to access it's '.h' files and such-- correct me if I'm wrong). But what does referencing a names开发者_运维问答pace do? I understand the 'using' declarative allows you to not qualify the namespace anymore-- is this 'referencing namespaces' just another way to do that?

To clarify by what I mean by 'referencing': I'm talking about when right clicking on a project in the solution explorer and selecting 'References' which then brings up the 'Property Pages' dialog and then finally selecting the 'Add New Reference...' button.

'Add a reference' in .NET is somewhat like #includeing in normal C++. It allows you to use classes and namespaces inside another .cs file, that is not in the project, e.g., system libraries.
If you're coding normal C++, don't worry about it.